Method and system for locating and correcting the orientation of an autonomous mobile object and a non-autonomous mobile object

Abstract

In a method of locating and orienting a first direction linked to the position and to the orientation of an autonomous first mobile object (M), such as a ship towing a marine geophysical prospecting cable, and a second direction formed by a non-autonomous second mobile object (Bj), such as a buoy at the trailing end of the towed cable, and at least one reference point on the first mobile object relative to a fixed reference radionavigation system comprising at least two reference beacons (Si, Si+1) the first mobile object (M) and the second mobile object (Bj) are respectively provided with a first communication device (MI) providing communications between the first mobile object (M) and the reference beacons (Si, Si+1) and a second communication device (MJ) providing communications between the first mobile object (M) and the second mobile object (Bj). They are further provided with a communication device (BIJ) providing communications between each reference beacon (Si, Si+1) and the second mobile object (Bj). Firstly, the position of the first mobile object (M) relative to the reference radionavigation system and the orientation of the first direction relative to the first mobile object (M) are determined. Then the position of the second mobile object (Bj) relative to the reference radionavigation system is determined. Finally, the angular offset between the first and second directions is determined, with a view to correcting the orientation of the first direction relative to the second direction.

We claim: 
     
       1. Method of locating or orienting a first direction linked to the position and to the oreintation of an autonomous first mobile object (M) and a second direction defined by a non-autonomous second mobile object (Bj) and at least one reference point on the first mobile object relative to a fixed reference radionavigation system comprising at least two reference beacons (Si, Si+1), the first mobile object (M) and the second mobile object (Bj) being respectively provided, on the one hand, with first communication means (MI) providing communications between the first mobile object (M) and the reference beacons (Si, Si+1) and second communication means (MJ) providing communications between the first mobile object (M) and the second mobile object (Bj), and, on the other hand, communication means (BIJ) providing communications between each refrence beacon (Si, Si+1) and the second mobile object (Bj), which method consists in: (a) determining the position of the first mobile object (M) relative to the reference radionavigation system and the orientation of the first direction relative to the first mobile object (M),   (b) determining the position of the second mobile object (Bj) relative to the reference radionavigation system,   (c) determining the angular offset between the first and second directions, with a view to correcting the orientation of the first direction relative to the second direction.   
     
     
       2. Method according to claim 1, wherein said first mobile object is a ship towing a marine geophysical prospecting cable and the second mobile object is a buoy at the trailing end of said cable. 
     
     
       3. Method according to claim 1, wherein, said reference radionavigation system being a circular type location radionavigation system, the aforementioned steps (a) and (b) of said method consist in executing the following location protocol: using the first communication means (MI) to interrogate each of the reference beacons (Si, Si+1) or a plurality of said reference beacons in order to establish from the round trip propagation time between the mobile (M) and each of the reference beacons (Si, Si+1) interrogated the successive distances (MSi) separating the first mobile (M) from each of the reference beacons (Si, Si+1),   determining the position of the reference point (R) on the first mobile (M) from the positions of the reference beacons (Si, Si+1),   using the communication means (BIJ) of the second mobile object (Bj) to receive the signal of frequency (FSi, FSi+1) transmitted in response to interrogation of at least one reference beacon (Si, Si+1) and to retransmit said signal of frequency (FSi, FSi+1) received by said communication means (BIJ) using said second communication means (MJ) to said first mobile (M) in order to determine from the time (Ti) at which each of the reference beacons (Si) is interrogated the length of the closed path (MSiBjM) formed by the respective elementary distances (MSi, SiBj, BjM) between the first mobile object (M), the reference beacon (Si) and the second mobile object (Bj),   using said second communication means (MJ) to interrogate said second mobile object (Bj) to determine the distance between the reference point on the first mobile object (M) and the second mobile object (Bj),   determining the distances (SiBj, Si+1Bj) between the second mobile object (Bj) and at least two reference beacons (Si, Si+1) by calculating the difference between the lengths of the corresponding closed paths (MSiBjM), (MSi+1BjM) and the distance (MBj),   determining the position of the second mobile object (Bj) relative to the reference radionavigation system by a circular type location method from the distances (SiBj, Si+1Bj) separating said second mobile object from the reference beacons of rank i, i+1.   
     
     
       4. Method according to claim 3, wherein retransmission to said first mobile (M) of the signal at frequency (FSi) received by said communication means (BIJ) by means of said second communication means (MJ) and/or interrogation of the second mobile object (Bj) by means of said second communication means (MJ) are effected at a low power level and at a carrier frequency different to the frequency (FSi, FSi+1) at which the reference beacons (Si), (Si+1) are interrogated. 
     
     
       5. Method according to claim 1, wherein, said reference radionavigation system being a hyperbolic type location radionavigation system, said steps (a) and (b) of said method consist in executing the following location protocol: using the first communication means (MI) to receive the sequence transmitted by each of the reference beacons (Si), (Si+1) to establish the difference (MSi-MSi+1) between the distance from the first mobile (M) to a first reference beacon (Si) and the distance from the mobile (M) to a second reference beacon (Si+1) for a plurality N of reference beacons (Si),   determining the position of the reference point on the first mobile (M) from the positions of the refrence beacons (Si, Si+1),   using the communication means (BIJ) of the second mobile object (Bj) to receive said sequence sent by each of the reference beacons (Si), (Si+1) and using said communication means (BIJ) to retransmit to said first mobile (M) a signal in response to transmission of the frequency (FS) by each reference beacon (Si) to determine the length of the composite path (Si, Bj, M) constituted by each respective elementary distance (SiBj, BjM), (Si+1Bj, BjM) between each reference beacon (Si), the second mobile object (Bj) and the first mobile object (M),   determining the position of the second mobile object (Bj) relative to the reference radionavigation system by a hyperbolic type location method from the difference (SiBj-Si+1Bj) between the distances separating said second mobile object (Bj) from the reference beacons (Si), (Si+1).   
     
     
       6. Method according to claim 5, wherein the retransmission by means of said second communication means (BIJ) to the first mobile (M) of a signal in response to transmission by each reference beacon (Si) is effected at a low power level and at a carrier frequency different to the frequencies (FSi) at which the reference beacons (Si) generating the transmit sequence transmit. 
     
     
       7. Method according to claim 6, wherein said retransmission is synchronized to said transmit sequence and is effected between the periods in which each reference beacon (Si) transmits. 
     
     
       8. Method according to claim 1, wherein with a view to enabling location and orientation of a first direction linked to the position and to the orientation of a first mobile object (M) and of a preferred second direction from a plurality of second directions defined by a plurality of second mobile objects (Bj) and at least one reference point on the first mobile object (M), each second mobile object (Bj) is provided with communication means (BIJ) providing communication between each reference beacon (Si, Si+1) and each second mobile object (Bj) and said first mobile object (M) is provided with second communication means (MJ) providing communication between said first mobile object (M) and each second mobile object (Bj). 
     
     
       9. Method according to claim 8, wherein said preferred direction is the mean direction for the set of second objects (Bj) relative to the reference point on the first mobile object. 
     
     
       10. System for locating and orienting a first direction linked to the position and the orientation of an autonomous first mobile object (M) and a second direction defined by a non-autonomous second mobile object (M) and at least one reference point on the first mobile object (M) relative to a fixed reference readionavigation system comprising at least two reference beacons (Si, Si+1), wherein, said radionavigation system being a circular type location radionavigation system, said first mobile object (M) comprises: first communication means (MI) enabling interrogation of each reference beacon (Si, Si+1) or a plurality thereof,   second communication means (MJ) enabling interrogation of said second mobile object (Bj) to determine the distance between the first mobile object (M) and the second mobile object (Bj), said second mobile object (Bj) comprising:   communication means (BIJ) providing communication between each reference beacon (Si, Si+1) and the second mobile object (Bj), said communication means (BIJ) enabling reception of the signal at frequency (FSi) transmitted by each reference beacon (Si, Si+1) and retransmission at the frequency (FBj) to said second communication means (MJ) of the first mobile (M) of a signal in response to the signal (FSi) received by said communication means (BIJ), said system further comprising at the mobile (M):   means for calculating the distances (MSi), (SiBj) between the first mobile object (M) and the second mobile object (Bj) and each beacon (Si), (Si+1),   means for calculating the position of said first mobile object (M) and said second mobile object (Bj) relative to the reference radionavigation system and the orientation of the second direction relative to the first direction.   
     
     
       11. System according to claim 10, wherein said first communication means (MI) and said second communication means (MJ) of the first mobile (M) are synchronized. 
     
     
       12. System according to claim 10, wherein the second communication means (MJ) of the first mobile (M) used to interrogate said second mobile (Bj) and the communication means (BIJ) enabling retransmission (MJ) from the first mobile (M) of the signal (FSi) in response to interrogation operate at the same carrier frequency (FBj). 
     
     
       13. System according to claim 12, wherein said communication means (BIJ) when used to retransmit to said first mobile (M) the signal in response to the signal transmitted at frequency (FSi) and said second communication means (MJ) of the mobile (M) operate at a low power level and at a carrier frequency (FBj) different to the frequency (FSi) of the signal transmitted by each reference beacon (Si, Si+1). 
     
     
       14. System for locating and orienting a first direction linked to the position and to the orientation of an autonomous first mobile object (M) and a second direction formed by a non-autonomous second mobile object (Bj) and at least one reference point on the first mobile object (M) relative to a fixed radionavigation system comprising at least two reference beacons (Si, Si+1), wherein, said radionavigation system being a hyperbolic type location radionavigation system, said first mobile object (M) comprises: first communication means (MI) for receiving signals at frequency (FSi, FSi+1) transmitted by each of the reference beacons (Si, Si+1) in a predetermined transmit sequence, said second mobile object (Bj) comprising communication means (BIJ) enabling successively reception of the signals transmitted at frequency (FSi, FSi+1) by each of the reference beacons (Si, Si+1) and retransmission of a signal at frequency (FBj) in response to transmission of the signals of frequency (FSi, FSi+1), said first mobile (M) further comprising:   second communication means (MJ) enabling reception of the signal at frequency (FBj) transmitted by the communication means (BIJ) in response to transmission of the signals at frequency (FSi, FSi+1) by the reference beacons (Si, Si+1), said system further comprising at the first mobile (M):   means for calculating the difference (MSi-MSi+1) between the distance from the first mobile (M) to a first reference beacon (Si) and the distance from the first mobile (M) to a second reference beacon (Si+1) for a plurality N of refrence beacons (Si), the differences (SiBj-Si+1Bj) between the second mobile object (Bj) and the reference beacons (Si, Si+1),   means for calculating the position of said first mobile object (M) and said second mobile object (Bj) relative to the reference radionavigation system and the orientation of the second direction relative to the first direction.   
     
     
       15. System according to claim 14, wherein said communication means (BIJ) when retransmitting to said first mobiel (M) the signal in response to transmission of the transmit sequence by each reference beacon (Si), (Si+1) operates at a low power level and at a carrier frequency (FBj) different to the frequency (FSi), (FSi+1) at which each of the beacons (Si, Si+1) transmits. 
     
     
       16. System according to claim 14, wherein said communication means (BIJ) of said second mobile object (Bj) enabling reception of the signal transmitted at frequency (FSi) by each reference beacon (Si, Si+1) and retransmission to said second communication means (MJ) of the first mobile object (M) comprises a transponder. 
     
     
       17. System according to claim 10, wherein the first mobile object (M) is a ship towing a marine geophysical prospecting cable and the second mobile object (Bj) is a buoy at the trailing end of a marine geophysical prospecting cable towed by the ship. 
     
     
       18. System according to claim 17, comprising a plurality of second mobile objects each of which is a buoy at the trailing end of a respective one of a plurality of marine geophysical prospecting cables towed by a ship.